Hydraulic fracturing is the propagation of fractures in a subterranean material such as rock by the use of a pressurized fluid. Induced hydraulic fracturing, or fracking, is a technique used to release petroleum, natural gas, or other substances for extraction from reservoir subterranean formations via a wellbore. The viscosity of the fluid used to perform the fracturing can alter the types of fractures formed in the subterranean formation. High-viscosity fluids are harder to pump to the fracturing site and more difficult to recover, but generally form large dominant fractures. Lower-viscosity fluids are easier to pump to the fracturing site and easier to recover, but generate cause smaller distributed fractures.
A proppant is a material that keeps an induced hydraulic fracture at least partially open during or after a fracturing treatment. Proppants can be transported downhole to the fracture using fluid, such as fracturing fluid or another fluid. A higher-viscosity fluid can more effectively transport proppants to a desired location in a fracture, especially larger proppants, by more effectively keeping proppants in a suspended state within the fluid. However, lower-viscosity fluids are less likely to dislodge proppants during recovery of the fluid.